In a telecommunication system voice quality enhancement VQE is required if a quality of the voice signal is degraded. An acoustic echo, a background noise or reverberations can form some of the possible causes for the signal degradation of the voice signal transported in a communication network. The voice quality enhancement VQE can be either applied in a terminal or in an intermediate network node of the communication network or both. Voice quality enhancement can significantly improve the quality of conversations by removing echo and background noise as well as by adjusting speech levels to achieve a consistent and comfortable listening experience to the users.
When voice quality enhancement VQE is applied in the telecommunication network this can be done by voice enhancement devices VED as specified for instance in ITU-TG.160. A voice enhancement device VED can provide certain signal processing network functions SPNFs such as noise reduction and acoustic echo cancellation in the digital transmission path of the communication network wherein said functions can perform voice quality enhancement functions on voiceband signals that can traverse the telecommunication network. The network can be a wired and/or wireless communication network.
In general, terminals of the communication network such as mobile phones can contain voice quality enhancement VQE models such as models for a noise reduction and acoustic echo cancellation. Acoustic echo cancellation models only operate on the digitally sampled audio signals of a communication device or a terminal. An acoustic echo cancellation model uses a transfer function of the acoustic environment from a loudspeaker to the microphone of the communication device which is estimated to cancel the received echo signals from the microphone signal. An acoustic echo cancellation model forms an essential part for providing a voice quality enhancement VQE function to any form of voice communication device of a network. Furthermore, a noise reduction module can adaptively reduce a background noise and effectively increase a SNR of the speech signal. In an acoustic environment there can be many sources of noise consisting of different spectrum characteristics, being either time invariant or time variant. Noise reduction provided by a noise reduction module has to be robust to all types of noise. Further, in conventional networks there are still many poorly designed terminals such as mobile phones which leave a high level of degradation of the voice signal. A poor design of the terminal can both come from a poorly designed acoustic interface as well as the use of poorly performing voice quality enhancement functions provided by the VQE modules. This leads to an overall poor conversation quality and promotes a need for network voice quality enhancement functions (VQEF) provided by a network elements of the communication network transporting the voice signal from one terminal to another terminal. A voice quality enhancement function provided by a network element can for instance compensate for residual acoustic echo from a mobile terminal of a user and can also perform additional noise reduction. Accordingly, conventional communication networks have as a common functionality voice quality enhancement functions (VQEF) provided by network elements of the communication network. This VQE-function can form a crucial function of the communication network and is a feature of the conversation quality offered by the respective network operator to the customers.
Audio signal processing in general and in particular voice quality enhancement (VQE) signal processing is to be performed as close as possible to the acoustic front end, i.e. the terminals to secure a high quality communication from the user's point of view. Voice quality enhancement functions can be better applied in a terminal since the audio signal can be encoded, modulated and transmitted over an unreliable communication channel such as a radio link which adds distortions to the transmitted signal such as a non-linearity and coding noise which reduces the performance of voice quality enhancement functions (VQEF) in particular of model based voice quality enhancements (VQE) processing in the network. On the other hand, an implementation of signal processing functions in a communication network is common in cases when no such capability is possible in the respective terminals, for example in a PSDN phone or if the capability offered in the terminal is of low performance. Accordingly, in conventional communication networks, “tandeming cases” can occur wherein to a speech signal a voice quality enhancement function (VQEF) is applied twice or more, i.e. both in the terminal as well as in at least one network element of the communication network. Tandeming of this type of non-linear and time-variant signal processing functions is not beneficial for the overall speech quality as perceived by the users. In most cases the speech signal is degraded due to this tandemed signal processing. Typical examples are degraded speech in uplink connections due to tandemed noise cancellation or poor double talk performance due to tandemed echo cancellation. Further severe artifacts such as clipping can be introduced into the processed speech signal which can lead to even more perceivable quality degradations for the users.
In ITU-T G.799.2 “Mechanism for Dynamic Coordination for Signal Processing Function” ITU-T SG16 a mechanism has been recently defined for implementation in terminals and network elements which can form a basis for a control of signal processing functions across terminals and network elements of a communication network. This conventional mechanism consists of adding a signaling in the communication network to inform whether voice quality enhancement VQE functions have been already applied to the signal. An appropriate protocol for wired and optical networks which is intended to implement this signaling mechanism is developed in ITU-T SG.11. A similar type of protocol is necessary for mobile communication networks. An overall quality perception increase of the users can be achieved when this conventional signaling mechanism is supported by mobile phones and mobile network elements. Signal processing functions not needed in a connection are switched off. The issue for which this signaling is provided is that the network does not know currently when the respective terminal exploits its signal processing capability. Hence, this conventional mechanism to avoid a voice quality enhancement VQE tandem fails or is missing if the signaling is not used.
The introduction of a signaling which makes the network elements of the communication network aware of a presence or absence of a signal processing capability of a voice quality enhancement device (VED) in the terminal has still many drawbacks. By introducing such a signaling all network elements of the communication network have to be aware of how to signal and how to interpret the received signaling in order to obtain an efficient processing. If an additional terminal employing this signaling is introduced a legacy voice enhancement device cannot interpret this signaling. Therefore, the introduction of such a signaling requires to update all existing voice enhancement devices VEDs of the network elements so that the voice enhancement devices are capable of interpreting this signaling. Accordingly, the implementation of such a control mechanism in existing communication networks requires high costs and efforts. In addition, any signaling mechanism and protocols has to be standardized first, especially given that communication networks consist o
Accordingly, it is a goal of the present invention to provide an improved apparatus and an improved method for providing voice quality enhancement VQE allowing, for example, to avoid a VQE tandem or VQE double processing.